Field of the Invention
The present invention relates to a vibration type actuator for generating a driving force by the vibration of a vibrator, and an optical device and an image pickup apparatus including the vibration type actuator.
Description of the Related Art
An ultrasonic motor has been conventionally used as a driving source for driving, for example, a camera lens, taking advantage of driving capability from low speed to high speed in a silent operation, and high torque output. In the ultrasonic motor disclosed in Japanese Patent No. 4652784, a vibrator is pressurized (or pressed) by a plate spring and an ultrasonic vibration is excited on the vibrator under the pressurized contact condition. An elliptic motion is generated on the vibrator at a portion in contact with a friction member, so that the vibrator is linearly driven. Since the plate spring includes an adjusting unit configured to adjust the amount of pressurizing (or pressing) force applied between the vibrator and the friction member, a pressurizing force can be adjusted upon assembling the ultrasonic motor. The drive efficiency of the vibrator can be improved by generating an appropriate friction force between the vibrator and the friction member.
In general, an optimum pressurizing force is set by the adjusting unit taking into account only the drive efficiency of the vibrator upon assembling the ultrasonic motor. In this case, a holding force generated by a friction force applied between the vibrator and the friction member may be insufficient if some impact is applied to a member to be driven or a change in attitude occurs thereon.